Wind and snow loading assessment
Wind and snow are the two environmental loads that most often govern a roof, a canopy or a light structure, and both change sharply with location, shape and exposure. We calculate them to the Eurocodes for buildings and structures across the UK.
When do I need a wind and snow loading assessment?
Whenever the environmental load is likely to govern, which covers canopies, car ports, agricultural and industrial buildings, rooftop plant and solar arrays, signage and lightweight or long-span roofs. It is also needed to confirm an existing roof can take something new added to it, such as solar panels or an extra storey.
Wind loading and why shape matters
Wind load is not a single number, it is a pressure that depends on where the building is, how exposed it is, how tall it is and, above all, its shape. We calculate wind actions to BS EN 1991-1-4 and the UK National Annex, starting from the basic wind speed for the location, adjusting for altitude, terrain and the surrounding ground, and then applying pressure coefficients that differ across the building. The result is not a uniform push, it is a pattern of pressures and suctions that peaks at corners, eaves, ridges and parapets, which is exactly where cladding and roofs tend to fail.
Suction is usually the problem, not pressure. Wind flowing over a roof or past a corner speeds up and drops the pressure, and that suction tries to lift the roof off and pull the cladding away from the building. Light roofs, canopies and open structures are especially vulnerable because there is little dead weight to hold them down, so the design often comes down to the fixings and the holding-down connections rather than the members. We identify the worst zones, calculate the peak suctions there, and check that the structure and its fixings resist uplift as well as gravity.
Snow loading and drifting
Snow load is calculated to BS EN 1991-1-3 and the UK National Annex, and the starting point is the snow load on the ground for the site, which increases with altitude and varies across the country. That ground load is then converted to a roof load using shape coefficients that depend on the roof pitch, because a steep roof sheds snow while a flat roof holds the full load. For most simple pitched roofs this gives a straightforward uniform load, but the interesting cases are where the snow does not lie evenly.
Drifting is where snow assessment earns its keep. Snow blows into valleys, piles up against parapets and taller adjacent buildings, and forms deep local drifts behind obstructions, and these drifted loads can be several times the uniform figure over a small area. That local concentration is what overloads a valley gutter beam or a canopy tucked against a taller wall. We calculate the drift cases as well as the uniform case, so the members that sit in the drift zones are designed for what actually lands on them, not an average that hides the peak.
When an assessment is needed and what you receive
A wind and snow assessment is often the deciding calculation for canopies, car ports, agricultural and industrial buildings, rooftop plant, solar arrays, signage and any lightweight or long-span roof, and it is frequently needed to justify an existing structure being reused or altered. It also underpins the check of an existing roof that is having something added to it, from a mansard to a bank of solar panels, where the question is whether the original structure can take the new environmental loads on top of the change.
We deliver a clear set of calculations stating the site parameters we used, the wind pressures and snow loads for each zone, and the load cases the structure has to be checked against, in a form your engineer, architect or Building Control can rely on. Where we are also doing the structural design we carry those loads straight through into the member and fixing checks. The environmental data varies across Europe as well as the UK, so we apply the correct national parameters for the country the structure is in, and we work with clients across both.
What we check.
The points our calculations resolve for a project like this.
- Basic wind speed adjusted for altitude, terrain and exposure to BS EN 1991-1-4
- Peak suction zones at corners, eaves, ridges and parapets
- Uplift and holding-down checks for light roofs, canopies and open structures
- Ground snow load converted to roof load by pitch to BS EN 1991-1-3
- Drift and asymmetric snow cases against parapets, valleys and taller buildings
- Correct national parameters for UK or European locations
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
When do I need a wind and snow loading assessment?
Whenever the environmental load is likely to govern, which covers canopies, car ports, agricultural and industrial buildings, rooftop plant and solar arrays, signage and lightweight or long-span roofs. It is also needed to confirm an existing roof can take something new added to it, such as solar panels or an extra storey.
Why is suction more important than wind pressure?
Wind speeding up over a roof or past a corner drops the pressure and creates suction that tries to lift the roof and pull cladding off the building. Light structures have little weight to resist this, so the uplift and the holding-down fixings often govern the design rather than the downward push.
What is snow drifting and why does it matter?
Snow blows into valleys and piles up against parapets and taller adjacent buildings, forming deep local drifts that can be several times the uniform snow load over a small area. That local peak is what overloads valley beams and canopies, so we calculate the drift cases as well as the even case to BS EN 1991-1-3.
Can you assess loads for a building outside the UK?
Yes. The Eurocodes are used across Europe with national parameters that set the wind and snow values for each country, so we apply the correct data for wherever the structure is. We provide calculations for clients across the UK.
Related in structural assessments & specialist services.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
Start a project